Abstract

We have used a thick‐walled aluminum enclosure to provide low‐frequency shielding for biomagnetic studies with SQUID magnetic gradiometers. The shield provides an attenuation proportional to frequency above 1/3 Hz. A 24‐hole fractional‐turn SQUIDgradiometer has been used in the enclosure to carry out studies of magnetoencephalography on humans. An ’’asymmetric’’ configuration for a second‐derivative gradiometer has been developed which provides a significant increase in sensitivity and resolution over more conventional symmetric arrays.